This process relates to a hard or preferably a medium density board made of lignocellulosic fibers, a process for the production of said fiberboard and a device for practicizing the process.
It is known from the Swedish Pat. No. 318,466 corresponding to the U.S. Pat. No. 3,386,879 that addition of a thermosetting resin and a thermoplastic resin in the production of a fiberboard improves the mechanical properties of the board, above all its internal bonding strength and its dimensional stability, and that addition of large amounts of resin will make it possible to remove the wet lap (board) from the hot press at a moisture content of 10-25 %, which will shorten the press cycle and consequently increase the capacity.
From the Austrian Pat. No. 298,037 published as patent on Apr. 25, 1972 correspondingg to the Canadian Pat. No. 948,825 it is known to vary the binder content in the core layer of particle boards, said core layer being able having a binder content of the innermost core zones being higher than that of the two outer core layer zones there also being surface zones at both sides of the board.
In the Norwegian Pat. No. 62,627 there is disclosed a process for the production of pressed products of fiber containing resin masses, fiber webs or fiber containing canals or parts thereof being provided with a resin and being brought into a pressing form so that the final product after pressing and curing is eliminated showing a continuous or stepwise change from high resin zones to low resin zones.
In the products of both the cited Austrian Patent and the cited Norwegian Patent there must be at least small narrow zones between the zones having different resin content, since one zone material is laid upon another zone material according to a dry method, there being no contact between the different zones other than that between the resin.